1. Field of the Invention
The present invention relates to a liquid crystal display, and a method of fabricating a liquid crystal display, which prevents light leakage from occurring near data lines in accordance with the rubbing direction of an alignment film.
2. Discussion of Related Art
A TFT-LCD (thin film transistor-liquid crystal display) is comprised of a TFT array plate in which a plurality of TFT's and pixel electrodes are arranged, a color filter plate consisting of color filters and common electrodes, and liquid crystal filling up a space between the TFT array and color filter plates. Both plates are equipped with alignment films as well as attached polarizing plates which polarize visible rays.
A TFT-LCD having the above-mentioned structure has an advantage merit in power consumption, compared to a cathode ray tube (CRT). Particularly, power consumption is the most important factor in a portable TFT-LCD.
Efficiency of a back light is reduced greatly during passing through a polarizing plate and color filters. For instance, only 38% of light energy penetrates through a commercial polarized plate, and 40% of light energy permeability of penetrates through color filters, and the contrast and color reproductivity are reduced if light energy the polarizing plate and color filters are increased. Instead, it is more efficient to increase the opening ratios which is the ratio of area which permits the transmission of light in a unit cell.
FIG. 1 shows a layout of a unit pixel of a conventional TFT-LCD.
FIG. 2 is a cross-sectional view of an LCD having a TFT with an inverse staggered structure according to a related art, which is bisected through the line I–I′ in FIG. 1.
FIG. 3 shows a cross-sectional view bisected through the line II–II′ in FIG. 1.
FIGS. 4A to 4C show cross-sectional views, which are bisected through the line II–II′ in FIG. 1, illustrating fabrication of an LCD according to a related art.
FIG. 5A shows a graph of equipotential potential lines between a TFT array plate and a color filter plate in an LCD according to a related art, wherein a predetermined voltage is applied to the plates. FIG. 5A also shows potential difference and the generation of light-leakage region B on data lines when light is cut off by liquid crystals between both plates. FIG. 5B shows a cross-sectional view of an LCD where a light leakage region is generated, which points out a problem of the related art.
Referring to FIG. 1 to FIG. 3, gate lines 10 are formed in a horizontal direction on a transparent substrate 1, which is a TFT array plate on which TFT's and pixel electrodes are arranged. Data lines 20, crossing the gate lines 10, are arranged in a perpendicular direction to the gate lines 10.
A gate electrode 14, extending from the gate line 10, is formed protruding in the same direction as the data line 20.
An active layer 12, beneath which a gate insulating layer 22 lies, is formed on the gate electrode 14. A channel region is defined in the portion of the active layer 12 corresponding to the gate electrode 14. At either side of the channel region in the active layer 12, a source region and a drain region are each defined.
A source electrode 16, connected to the source region of the active layer, and a drain electrode 18, connected to the drain region of the active layer, are formed in the same direction as the gate line 10 is aligned. The source electrode 16 and drain electrode 18 each protrude from the data line 20.
A passivation layer 24 covers the above structure. A contact hole exposing the drain electrode 18 is formed in the passivation layer 24. And, a pixel electrode 30 which is connected to the drain electrode 18 and covers the contact hole is formed on the passivation layer 24.
The pixel electrode 30, beneath which the passivation layer 24 lies on the data line 20, may have a structure such that the pixel electrode 30 partially overlaps the data line 20 and generally the width of the overlapped area, which is designated by the reference sign “A”, is under 1.5 μm, in order to increase the opening ratio. The reference numeric 32 indicates an opening of a black matrix (hereinafter abbreviated BM) 29 of a color filter plate m which is shown in FIGS. 5A–B. Light rays are actually transmitted through the opening.
A process of fabricating an LCD having the above-described structure according to a related art is explained in the following description.
Referring to FIG. 1, FIG. 2 and FIG. 4A, after a metal layer has been formed by sputtering Al, Mo or the like on a transparent substrate 1 such as glass, in which gate and data lines are defined, gate lines 10 are formed by patterning the metal layer. In this case, a gate electrode 14 is also patterned which protrudes from the gate line 10 as soon as the gate line 10 is patterned.
After a gate insulating layer 22 is formed to cover the gate electrode 14, an intrinsic amorphous silicon layer and a silicon layer to which an impurity such as P is added to work as an ohmic contact layer are deposited successively, and an active layer is formed by patterning the amorphous silicon layer and the impurity-contained silicon layer.
After a metal layer is formed on the above structure, data lines 20 are patterned by etching the metal layer. When the data lines 20 are patterned, source and drain electrodes 16 and 18 connected to the source and drain regions respectively are also patterned. The source and drain electrodes 16 and 18 are arranged to overlap the gate line 10.
Although not shown in the drawing, the impurity-containing silicon layer is etched using of the source and drain electrode patterns as a mask to divide the ohmic contact layer inserted between the active layer and the source/drain electrodes 16 and 18, into the portions for the source and drain electrodes.
Referring to FIG. 2 and FIG. 4B, a passivation layer 24 is formed on the above structure by depositing by CVD an insulating layer of silicon nitride or the like which has a low dielectric constant.
Referring to FIG. 2 and FIG. 4C, a contact hole exposing the drain electrode 18 is formed in the passivation layer 24.
After ITO (Indium Tin Oxide) has been deposited on the passivation layer 24, a pixel electrode 30 is formed by patterning the ITO to be connected to the drain electrode 18. The pixel electrode 30, as mentioned in the above explanation, has a structure overlapping with the data line 20. The width of the overlapped area A is less than about 1.5 μm.
Thus, a TFT array plate, on which TFT's and pixel electrodes are arranged according to a related art, is completed.
Referring to FIG. 5B, after liquid crystals 28 have been injected between the TFT array plate  and the color filter plate m in which color filters and black matrix 29 are fabricated, an LCD according to the related art is completed by carrying out a sealing process. An alignment film (not shown in the drawing) is formed on the color filter plate m and the TFT array plate 
Liquid crystals between the color filter and TFT array plates are aligned uniformly by carrying out a process of rubbing the alignment film with cloth.
It has been known that the LCD of the related art which has the above-mentioned structure normally has no problem of light leakage, as the data line and the pixel electrode overlap each other partially. Unfortunately, however, when voltage is applied between the color filter and TFT array plates m and  the light leakage problem does exist if that the overlap area between the data line and the pixel electrode is under 1.5 μm, as explained herein with reference to FIG. 5A and FIG. 5B.
FIGS. 5A and 5B show a pattern of cutting off light due to the liquid crystal function when voltage is applied between the color filter and TFT array plates m and  which operate in a normally white mode, wherein the data line 20 is overlapped by the pixel electrode 30 to a width of 1.5 μm in the TFT array plate of the related art. Curves between both plates m and  are equipotential lines. Liquid crystals react with the equivalent potential lines perpendicularly for the most part while the curves are slanted on the data line 20, due to the potential difference. FIG. 5A also shows the graph “P” indicating the permeability of light in the device.
Referring to FIG. 5A, when voltage is applied between both plates m and  the equipotential lines are deeply distorted, as the data line voltage influences the voltage applied to the liquid crystals. This influence distorts the working orientation of the liquid crystals to be slanted, and also generates a region in which the light permeability is abruptly increased. This region lies on the pixel electrode and extends 1 μm to 2 μm away from the area which is overlapped with the data line 20. In other words, the region includes the area overlapped with the data line 20, and the area designated by the reference indicator B in FIGS. 5A–B.
But, all of the above-mentioned light-transmitting region, which is the part with the permeability peak in the graph “P” in FIG. 5A, does not influence the image quality. Namely, the overlap region (1.5 μm), at which the data line and the pixel electrode overlap each other, does not influence the image quality directly, as the area is overlapped so as not to transmit the light. The other region B, in which the data line is not overlapped by the pixel electrode, actually transmits the light to have an effect on the image quality.
The above light leakage region B, which has no relation with the polarity of the voltage applied to the pixel electrode adjacent to the data line, may be generated at the right or left in accordance with the rubbing direction of the alignment film.
Unfortunately, the product quality is reduced due to the generation of the light leakage region which is produced by the transmission of light through the area B separated from the overlap area of 1.5 μm, between the data line and the pixel electrode, where the liquid crystals take on a slanted orientation because of the potential difference.